Electrokinetic pump designs and drug delivery systems

ABSTRACT

One embodiment of the present invention provides a piston assembly having a piston housing filled with an electrolyte; a housing within the piston housing that divides the piston housing into a first portion and a second portion, the housing having apertures, a shaft connecting the housing to a piston head outside of the piston housing; and a porous material inside of the housing in contact with the electrolyte. Additionally, there are provided a method for filling the delivery chamber with a delivery fluid by withdrawing the piston head from within the delivery chamber. Yet another embodiment provides a method for filling a fluid delivery assembly by withdrawing a shaft from within the fluid delivery assembly to simultaneously displace a moving pump element within the delivery chamber and bypass fluid around a housing in the pump chamber.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 60/739,390 filed Nov. 23, 2005, titled, “Electrokinetic Pump Designs and Drug Delivery Systems” which is incorporated herein by reference in its entirety. This application is related to the following co-pending patent applications: U.S. application Ser. No. (not yet assigned) filed herewith titled, “Electrokinetic Pump Designs and Drug Delivery Systems” (Attorney Docket number 10076-705.201); U.S. application Ser. No. 10/198,223, filed Jul. 17, 2002 titled, “Laminated Flow Devices”; U.S. application Ser. No. 10/273,723 filed Oct. 18, 2002 titled, “Electrokinetic Device Having Capacitive Electrodes”; U.S. application Ser. No. 10/322,083 filed Dec. 17, 2002 titled, “Electrokinetic Device Having Capacitive Electrodes” and U.S. application Ser. No. 11/112,867 filed Apr. 21, 2005 titled, “Electrokinetic Delivery Systems, Devices and Methods,” each of which are incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

Pumps and pumping systems exist for the delivery of various fluids. A variety of pumps are used in a number of various different configurations and uses. Pumps are used for infusion of drugs or delivery of drugs into mammals, the sterility of the drugs is very important. In addition, contamination of the drug or delivery fluid from the pump system should be reduced or eliminated. Additionally, it remains an important aspect to minimize contact between the drug to be delivered and the internal components of the pump being used to deliver the drug. Filling or preparing the drug or fluid for delivery should not be time consuming. These and other difficulties are encountered using conventional filling and pumping systems.

Related U.S. application Ser. No. 11/112,867 filed Apr. 21, 2005 titled, “Electrokinetic Delivery Systems, Devices and Methods,” discloses a technique for filling a pump with fluid for delivery. This technique involves operating the pump system in reverse to draw the delivery fluid into the pump. Then, after filling the pump with the delivery fluid, the pump direction is reversed and the delivery fluid is delivered from the pump. Reversing pump direction may be a good solution for small amounts of fluid or for pump configurations that have a very high linear flow rate. However, the time requirements for loading large volumes of delivery fluid using this technique may be prohibitive for time conscious applications and problematic for later pump operation.

What are needed are improved techniques for providing the delivery fluid into the pumping system. The pump filling procedures should be simple and require small amounts of time.

SUMMARY OF THE INVENTION

One embodiment of the present invention provides a piston assembly having a piston housing filled with an electrolyte; a housing within the piston housing that divides the piston housing into a first portion and a second portion, the housing having apertures that provide fluid communication between the first portion and the second portion; a shaft connecting the housing to a piston head outside of the piston housing; and a porous material inside of the housing in contact with the electrolyte.

In one aspect, the porous material is a porous dielectric material adapted for operation as part of an electrokinetic pump. In another aspect, there is a sealing element around the piston head or the housing. In yet another aspect, there is a second shaft connecting the housing to a handle outside of the piston housing. In another aspect there is a valve within the second shaft wherein actuation of the valve provides a flow path between the first portion and the second portion. In yet another aspect, the flow path from one side of the housing to the other side of the housing includes a bypass through the porous material contained in the housing. In another aspect, the valve is actuatable from a handle attached to the second shaft. In another aspect, the shaft extends through a wall in the piston housing. In another aspect, the sealing element around the material housing seals the housing to a wall of the piston housing. In another aspect, there is an electrode in the first portion and an electrode in the second portion. In one embodiment, the electrodes have a double layer capacitance of greater than 10⁻⁴ microfarad/cm².

In another embodiment of the invention, there is provided a pump having a delivery chamber, a pump chamber and a wall separating the pump chamber from the delivery chamber; a piston assembly having a piston head in the delivery chamber, a housing in the pump chamber and a shaft connecting the piston head to the housing and passing through the wall separating the pump chamber from the delivery chamber; and a dielectric material in the housing.

In one aspect, there is a pair of electrodes in the pump housing. In one aspect, there is one electrode is on each side of the housing. In one embodiment, the pair of electrodes are made from a material selected to electrokineticly move a fluid in the pump chamber. In one aspect, the delivery chamber and the pump chamber are in a single housing. In another aspect, the housing divides the pump chamber into a first portion and a second portion. In yet another aspect, there is provided apertures in the housing that provide fluid communication between the first portion and the second portion. In another aspect, there is an electrolyte in the pump chamber. In a further aspect, each electrode in the pair of electrodes has a double layer capacitance of more than 10⁻⁴ microfarad/cm². In yet another aspect, there is a bypass valve in the shaft that provides a fluid pathway from one side of the housing to the other side of the housing. In one aspect, the bypass valve in the shaft that provides a fluid pathway from the first portion to the second portion. In another aspect, the delivery chamber is filled with a delivery fluid by relative movement between the pump chamber and the delivery chamber. In another aspect, application of an electric field across the electrodes moves the fluid in the pump chamber from one side of the housing to the other side of the housing. In one aspect, application of an electric field across the electrodes moves the piston head in the delivery chamber. In another aspect, application of an electric field across the electrodes moves the housing relative to the pump chamber.

In another embodiment, there is provided a method for operating a fluid delivery system by inserting a piston assembly into a delivery chamber, the piston assembly having a pump housing, a piston head outside of the pump housing and attached to a shaft extending through a wall in the pump housing, a housing attached to the shaft and between electrodes in the pump housing; and filling the delivery chamber with a delivery fluid by withdrawing the piston head from within the delivery chamber. In one further aspect, the method fixes the position of the pump housing relative to the delivery chamber. In another aspect, there is provided the step of advancing the piston head in the delivery chamber by moving fluid in the pump chamber. In one aspect, moving fluid within the pump chamber comprises electrokineticly moving fluid through the housing. In another aspect, moving fluid within the pump chamber comprises providing an electric field between the electrodes. In yet another aspect, the filling step comprises withdrawing the pump assembly.

In another embodiment, there is a method for operating a fluid delivery assembly having a pump chamber and a delivery chamber by withdrawing a shaft from within the fluid delivery assembly to simultaneously displace a moving pump element within the delivery chamber and bypass fluid around a housing in the pump chamber.

In one aspect, withdrawing a shaft from the pump assembly introduces a delivery fluid into the delivery chamber and into contact with the moving pump element. In another aspect, advancing the moving pump element in the delivery chamber by applying an electrical field across electrodes in the pump chamber and on either side of the housing. Still another aspect provides electrokineticly moving fluid in the pump chamber to dispense fluid from the delivery chamber. In still another aspect includes actuating a bypass in the shaft during the withdrawing step.

INCORPORATION BY REFERENCE

All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth with particularity in the claims that follow. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which:

FIG. 1 is section view of an exemplary pump system.

FIGS. 2A-2E illustrate details for the loading and delivery of fluid using the pumping system 900.

FIGS. 3A-3E illustrate details for the loading and delivery of fluid using the pumping system 1000.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 will be described to provide an understanding of the basic components and operation of a typical fluid delivery system. FIG. 1 illustrates a cross section view of a fluid delivery system 1. The fluid delivery system has a first chamber 30, a second chamber 32 and a third chamber 35. A flow through pump element 20 (such as electrokinetic pump, as shown in FIG. 1) separates the first chamber 30 from the second chamber 32. A moveable pump element 40 (such as a floating piston, as shown) separates the second chamber 32 from the third chamber 35. While in this illustrative embodiment the moveable element 40 is a floating piston, any device that provides a moveable barrier may be used as will be illustrated in the examples that follow. In this embodiment, the first, the second and the third chambers are within a single housing 15. Seals 42 are used to seal the moveable pump element 40 as it moves within the housing 15. An outlet 45 provides communication between the third chamber 35 and the exterior of housing 15. An outlet 55 provides communication between the second chamber 32 and the exterior of housing 15. In this embodiment, a valve 60 separates the second outlet 55 from the exterior of housing 15.

As illustrated, a conduit 71 connects the outlet 55 to the opening 70. A valve 60 in the conduit 71 controls fluid flow from the outlet 55 to the opening 70. The valve 60 has a disc 62, stem 64, a spring 66 and a disc or seal 68. Seats 72, 74 in the housing are shaped to seal with, respectively, discs or seals 62, 68. Valve 60 is shown in the closed position where spring 66 holds discs 68, 62 in place against seats 72, 74. In this embodiment, conduit 71 and valve 60 are disposed in a wall of housing 15. Other configurations are possible such as a separate valve assembly that attaches directly to port 55 or a valve/conduit configuration that ports through the pump element 20 rather than around the pump element 20 as shown.

In the illustrated embodiment, the first chamber 30 contains a moveable pump element 82 (i.e., a diaphragm adjacent the pump element 20). The first chamber 30 also contains a vent 75, if needed to ensure free movement of the moveable element 82. The space between the diaphragm 82 and the pump element 20 contains a buffer or pump fluid 80 that is selected to operate with the type of pump element used. If the pump element 20 is an electrokinetic pump, then the buffer 80 would be an electrolyte selected to operate with the electrode and porous material materials and desired operation of the pump. Examples of specific electrolytes and other details of electrokinetic pumps are described in co-pending and commonly assigned patent application serial numbers U.S. application Ser. No. 10/198,223, filed Jul. 17, 2002 titled, “Laminated Flow Devices”; U.S. application Ser. No. 10/273,723 filed Oct. 18, 2002 titled, “Electrokinetic Device Having Capacitive Electrodes”; U.S. application Ser. No. 10/322,083 filed Dec. 17, 2002 titled, “Electrokinetic Device Having Capacitive Electrodes” and U.S. application Ser. No. 11/112,867 filed Apr. 21, 2005 titled, “Electrokinetic Delivery Systems, Devices and Methods,” each of which are incorporated herein by reference in its entirety.

The pump element 20 is connected to supporting electronics 5 by electrical connectors 26. The supporting electronics 5 may be altered depending upon the type of pump element(s) used but will generally include a user control interface 6, electronic control circuitry 8 and a power supply 10. The user control interface 6 may be a touch screen or other input means to allow a user to operate the delivery system, select a program or otherwise provide programming instructions to the system. The electronic control circuitry contains the programming instructions needed to translate the user inputs into commands to operate the pump element. The electronic control circuitry also regulates the power supply to achieve user desired pumping characteristics such as flow rate and delivery timing. The power supply 10 may be a battery or the delivery system may be plugged into an electrical supply. The supporting electronics are conventional and will be understood by those of ordinary skill in the art.

An exploded view of one type of pump element 20 is shown in FIG. 1. The pump element 20 shown in FIG. 1 is an electrokinetic pump element. Electrokinetic pump element contains a porous material 22 between two capacitive electrodes 24. One example of a suitable porous material is a nanopore filter. The capacitive electrodes are connected to the supporting electronics 5 by electrical connectors 26. The pump element contains a pump fluid or buffer 80 that is moved through the porous material 22 from one electrode towards the other electrode depending on how a charge is applied between the electrodes 24. The electrokinetic flow produced by the pump element 20 may be in one direction (from one electrode to the other electrode) or may alternate directions of flow (towards one electrode and then away from that electrode and towards the other electrode). Examples of electrokinetic pumps configurations, electrolytes, electrodes, porous materials (also referred to as porous dielectric materials) and other details of are described in co-pending and commonly assigned patent applications: U.S. application Ser. No. 10/198,223, filed Jul. 17, 2002 titled, “Laminated Flow Devices”; U.S. application Ser. No. 10/273,723 filed Oct. 18, 2002 titled, “Electrokinetic Device Having Capacitive Electrodes”; U.S. application Ser. No. 10/322,083 filed Dec. 17, 2002 titled, “Electrokinetic Device Having Capacitive Electrodes” and U.S. application Ser. No. 11/112,867 filed Apr. 21, 2005 titled, “Electrokinetic Delivery Systems, Devices and Methods,” each of which are incorporated herein by reference in its entirety.

Optionally, a storage fluid 50 fills the second chamber. The storage fluid 50 may be a fluid used to maintain the integrity of the pump element 20 during storage or prior to operation. The storage fluid 50 may be the same or different than the fluid 80 stored in the first chamber. The storage fluid 50 may also be a pump fluid (i.e., such as electrolyte suited to operation in an electrokinetic pump) moved by operation of the pump element 20. A delivery fluid 36 is stored in the third chamber 35. In some embodiments, the delivery fluid is a drug, a pharmacological or therapeutic agent, or other substance to be delivered by operation of the pump element 20. FIG. 1 also illustrates a conventional syringe 90 is also illustrated having a body 91 with a tip 92. A plunger 93 is attached to handle 95 by shaft 94 is disposed within the body 91.

Pump system 1 provides one solution to loading the pump system without the use of the pump element 20 by bypassing the pump element. Additionally, the pump element 20 remains in a fixed position within the pump housing during both filling and pumping operations. The pump systems 900 and 1000 provide an alternative apparatus and method for filling and delivering fluid. In contrast to the fixed pump element fluid system 1, the pump element in pump systems 900, 1000 moves within the pump housing during fluid delivery operations. The pump element in fluid system 1000 also moves during pump filling operations. These and other details of the pump systems 900, 1000 are described below.

FIGS. 2A-D and FIGS. 3A-E illustrate pumping systems 900, 1000. Novel piston assemblies are at the heart of the systems. The piston assemblies are designed to move within another pump component to deliver fluid. Piston assembly 970 (illustrated in FIG. 2B) and piston assembly 990 (illustrated in FIG. 3B) have several common components. A piston head 972 is connected to a housing 980 by a shaft 976. The housing 980 contains a porous material 984 and a plurality of apertures 982 to allow fluid flow through the housing 980 and the porous material 984. In one embodiment, the porous material 984 is a dielectric material adapted for operation as part of an electrokinetic pump. Examples of porous dielectric materials described in the co-pending patent applications described above. A sealing element or elements 974 are provided around the perimeter of the piston head 972. The piston head 972 is sealed within a delivery chamber that is separate from the pump chamber (i.e., delivery chamber 910 in FIG. 2A) or integrally formed with the pump chamber (i.e., delivery chamber 1010 in FIG. 3A). One or more sealing elements 978 is provided around the perimeter of the housing 980. The housing 980 is sealed within the pump chamber using sealing elements 978 as shown in FIGS. 2A and 3A.

FIG. 2A illustrates a pump 900 that includes a delivery chamber 910, a pump chamber or piston housing 950 and a wall 931 separating the pump chamber 950 from the delivery chamber 910. The piston housing 950 is filled with a suitable electrolyte 80. A piston assembly 970 has a piston head 972 in the delivery chamber 910 (i.e., outside of the pump housing 950), a housing 980 in the piston housing or pump chamber 950 and a shaft 976 connecting the piston head 972 to the housing 980. The shaft 976 passes through the wall 931 separating the pump chamber 950 from the delivery chamber 910. As shown in FIG. 2B, the housing 980 divides the piston housing 950 into a first portion 950A and a second portion 950B. A pair of electrodes 924 are in the pump housing 950 where there is one electrode 924 is on each side of the housing 980. There is an electrode 924 in the first portion 950A and an electrode 924 in the second portion 950B. In one embodiment, each electrode in the pair of electrodes has a double layer capacitance of more than 10⁻⁴ microfarad/cm². A porous material 984 is contained inside of the housing 980 and in contact with the electrolyte 80. The housing 980 has apertures 982 that provide fluid communication between the first portion 950A and a second portion 950B. The housing 980 is sealed within the piston housing 950 using sealing element 978.

The housing 910 includes an outlet 945 and an interior space 915. The interior space 915 is sized and shaped to sealingly receive the piston head 972. The piston housing 950 is adapted for pumping operations using the piston assembly 970. The housing 950 includes electrodes 924 positioned on either end of housing interior. The piston assembly 970 is disposed within the housing 950 with shaft 976 extending through a sealed opening 943. The housing 950 is inserted into the interior space 915 and the piston 972 is advanced against the interior 915 adjacent the outlet 945. The pump system 900 is now ready for filling.

The pump system 900 is filled by attaching a vial 105 or other suitable container to the outlet 1045 and then withdrawing the piston housing 950 from the delivery interior 915 as indicated by the arrow in FIG. 2C. The relative movement of the pump chamber 950 to the delivery chamber 910 draws the delivery fluid 36 from vial 105 through the outlet 945 and into the interior 915 as shown in FIG. 2C. Next, the vial 105 is removed and a delivery device, such as an infusion set 96, is attached to outlet 945. An optional purge or prime procedure is illustrated in FIG. 2D. Before attachment of the delivery device, after attachment of the delivery device or both before and after attachment of the delivery device the system may be primed or purged of air by advancing the piston housing 950 relative to the delivery chamber 910 as indicated by the arrows in FIG. 2D.

Prior to commencement of pumping, the position of the piston housing 950 is fixed relative to the delivery chamber 910. In one embodiment, the housings 910, 950 are fixed when feature 912 on delivery chamber 910 and feature 934 on chamber 950 are locked in place using bars 492 and spaces 494 within the frame 490 as illustrated in FIG. 2E.

Pumping begins when an electric field is applied across electrodes 924. Application of an electric field across the electrodes 924 moves electrolyte 80 in the pump chamber 950 from one side of the housing 980 (i.e., the portion 950B) to the other side of the housing (i.e. the portion 950A). In one embodiment, the electrolyte 80 is moved electrokineticly through the apertures 982 and the porous material 984 from one electrode 924 towards the other as indicated by the arrows in FIG. 2E. This movement of the electrolyte decreases the volume of the portion 950B and increases the volume of the portion 950A. Increasing volume of portion 950A moves the housing 980 and the piston head 972 towards the outlet 945 which in turn expels delivery fluid 36 out through outlet 945.

Turning now to FIGS. 3A and 3B that illustrate the pumping system 1000. The pumping system 1000 includes a delivery chamber 1010 and a pump chamber 1020 within a single housing (i.e., the pump housing 1005). The delivery chamber 1010 has an outlet 1045 and a vent 1012. A vial 105 filled with a delivery fluid 36 is attached to outlet 1045 and the pump system 1000 is ready for filling. The piston assembly 990, illustrated in FIG. 3B, is disposed within the pump housing 1005. The piston assembly 990 is arranged within a piston housing or pump chamber 1020 filled with an electrolyte 80. A housing 980 within the piston housing divides the piston housing into a first portion 980A and a second portion 980B and maintained by seals 978. The housing 980 has apertures 982 that provide fluid communication between the first portion 980A and the second portion 980B. The housing 980 contains a porous material 984 in communication with the electrolyte 80. The porous material 984 may be a porous dielectric material adapted for operation as part of an electrokinetic pump. A pair of electrodes 1024 are provided in the pump chamber 1020. One electrode 1024 is provided on each side of the housing 980 (i.e., one electrode in the first portion 980A and one electrode in the second portion 980B). In the illustrated embodiment, the electrodes, dielectric material and electrolyte are selected to provide electrokinetic movement of the electrolyte within the pump chamber and through the housing 980. In one embodiment, the electrodes are made of a material having a double layer capacitance greater than 10⁻⁴ microfarads/cm².

A shaft 976 connects the housing 980 to a moveable pump element (here, a piston head 972) and a handle 994 outside of the piston housing 1020. The shaft 976 may be a single piece as illustrated or be formed of multiple pieces. An example of a multiple piece shaft would be a first shaft connecting the housing 980 to the piston head 972 and a second shaft connecting the housing 980 to the handle 994. Sealing elements 1018, 1028 maintain the fluid integrity where the shaft passes through the pump chamber walls via openings 1014, 1026. The piston assembly 990 also includes a bypass feature not found in piston assembly 970. The piston assembly 990 includes a valve 988 within the shaft 976 that provides a fluid pathway from one side of the housing 980 (i.e., the first portion 980A) to the other side of the housing 980 (i.e., the second portion 980B) without passing the fluid through the porous material 984. The valve 988 or fluid path through the shaft 976 provides a bypass through the porous material contained in the housing without requiring operation of the electrodes or inducing flow though the material 984. The valve 988 is actuatable from a handle 994 attached to the housing 980. In the illustrated embodiment, a button 996 located on the handle 994 is used to depress the spring in 986, open valve 988 and to allow fluid flow through the shaft 976 around the housing 980.

FIG. 3C illustrates a method of operating a fluid delivery system 1000 having a pump chamber 1020 and a delivery chamber 1010. Filling is performed by withdrawing the shaft 976 within the fluid delivery assembly to simultaneously displace a moving pump element within the pump chamber (i.e., the piston head 972) and bypass fluid around the housing 980 in the pump chamber 1020 (as shown by the arrows in pump chamber 1020). FIG. 3C also illustrates that the button 996 in handle 994 is depressed (thereby opening the bypass with valve 988) while the handle 994 is withdrawn. Once a vial 105 or other suitable container is attached to the outlet 1045, withdrawing the shaft 976 from the pump assembly also introduces the delivery fluid 36 into the delivery chamber 1010 and into contact with the moveable pump element (i.e., the piston head 972). When the button 996 is depressed the bypass valve 988 allows fluid allows buffer 80 to pass from one side of the housing 980 to the other side as illustrated by the arrows. Now that buffer 80 may move freely within the pumping chamber 1020, the handle 994 is withdrawn thereby withdrawing piston head 972 within the delivery chamber 1010. This action draws delivery fluid 36 into the delivery chamber the outlet 1045.

As shown in FIG. 3D, when the filling operation is complete, the button 996 is released. When button 996 is released, action by spring 986 forces the valve 988 closed thereby preventing further passage of buffer 80 through the bypass valve as illustrated in FIG. 3D. A delivery device is attached to the outlet 1045. In the illustrated embodiment, the delivery device is an infusion set 96 having an outlet 1080.

Pumping begins with the application of an electric field across the electrodes 1024 that moves the electrolyte 80 in the pump chamber from one side of the housing 980 to the other as indicated by the arrows inside chamber 1020. The movement of electrolyte from portion 980B into 980A moves the housing 980 and the piston head 972 towards the outlet 1045 by increasing the volume of portion 980A while decreasing the volume of the portion 980B. In the illustrated configuration, when an electric field is applied across electrodes 1024, electrolyte 80 is moved electrokineticly through the apertures 982 and the porous material 984 from one electrode 924 towards the other electrode 1024 as indicated by the arrows inside chamber 1020. As such, movement of the buffer 80 through the apertures 982 moves the housing 980. Movement of the housing 980 in turn advances the piston head 972 to expel delivery fluid 36 out through outlet 1045 and delivery device 96.

The foregoing illustrative embodiments have used certain terms to provide an explanation of the principal involved or operation of the illustrated systems. It is to be appreciated that numerous alternatives for components and elements are possible. For example, the pump element and components in the pump chamber may form an electrokinetic pump as described but may be reconfigured to accommodate the use of diaphragm pumps, piston pumps, and piezoelectric pumps. The supporting electronics 5 and electrical connectors 26 would be modified as needed according to the type of pump element and other components used. Additionally, many of the illustrative configurations described the use of a movable pump element such as piston head 972. It is to be appreciated that the movable pump element may be a piston or a diaphragm and that both may be used in a single system (i.e., as illustrated in FIG. 1). The diaphragm may be a ‘rolling’ type diaphragm. Rolling diaphragms have a convolute that allows predictable travel of the diaphragm. While a rolling diaphragm does have advantages, the invention is not so limited and other types of diaphragms and moveable pump elements may be used.

The process of drug aspirating and air purging has been shortened in many of the illustrative descriptions. For configurations describing filling the pump with delivery fluid, the description simply indicates to pull back on a handle or pump housing to drawn drug or delivery fluid in. Those of ordinary skill will appreciate that this is an abbreviated instruction. Like any drug aspiration process, trapped air is vented before the drug is delivered. As such, the full process includes drawing drug in by pulling back on the handle or housing, then while holding the unit with the drug exit port at the top, flick the unit to release bubbles, and then press the syringe handle in to purge air out of the unit. The process is repeated if necessary until all visible air is removed and the unit is filled with the desired amount of drug. This process is identical to the typical method used by medical practitioners to aspirate drug into syringes and purge air.

A generic infusion set 96 is described and many of the pump system embodiments are represented as connected to an infusion set. While not illustrated in every embodiment, a similar configuration of an infusion set connection or other suitable delivery device can be inferred for all pump system embodiments. Alternatively, the delivery fluid 36 or drug may be dispensed without an infusion set such as, for example, when it is delivered directly into a canula or elsewhere.

The use of liquid and/or air seals have been illustrated in some embodiments. In some embodiments, those components requiring seals (piston head 972, housing 980, etc.) have two o-ring seals while in other embodiments only one o-ring seal shown. Two seals are typically used in medical syringes and have thus been shown in pairs on most of the pistons described herein. It is to be appreciated that one or more o-rings may be used, however, or alternate types of seals may be employed.

Any of the configurations may be partially filled with drug or delivery fluid to any desired amount. Additionally, in some embodiments, the portion of pump housing (i.e. delivery chambers 910, 1010) that stores the delivery fluid would be transparent and graduated to allow visibility and amount of the delivery fluid 36 present. In addition, a transparent housing generally would also allow visibility of any air that needs to be purged during the filling process. Volumetric increment markings may also be appropriately provided on the pump housing by printing, stamping, embossing, painting or otherwise indicating the contents of the delivery fluid 36 within a drug or delivery chamber.

One benefit of the pumping systems described herein is that these systems provide indirect pumping of delivered liquids regardless of the type of pump used for pump element 20 or pumping configuration. The pump components are contained within piston housing 950 or pump chamber 1020 and as the descriptions above make clear, the delivery fluid 36 does not pass through any pump mechanism and is actually separated from the pump components. As such, the pump systems described herein can be reused without concern of contamination of a deliverable fluid via contact with previously contacted surfaces of the pump mechanism (e.g. interior of pump, piston pump, etc.) by previously used delivery fluids. Another advantage is the decreased likelihood of damage to fluids that are susceptible to mechanical and/or chemical degradation such as long chain protein molecules and peptides. Mechanical actions including compression, shearing, and extrusion, as well as exposure to electrical currents can cause molecular level damage to some fluids. By obviating the need for the fluids to pass through the pump mechanism, concern over pumping damage to these compounds is diminished.

The term buffer has been used throughout the description. Buffer refers to any suitable working fluid that may be used by a particular pumping system. In many pumping system embodiments, the buffer or working fluid is any fluid having a viscosity low enough to be pumped through the pump element. In those embodiments where the pump element is an electrokinetic pump, working fluid is an electrolyte suited to the specific electrodes and dielectric material used by the electrokinetic pump. In one specific embodiment, the electrolyte is a buffered electrolyte. One buffered electrolyte is Tris Sorbate (sp?). [DEON: Please confirm. Are there other specific electrolytes or pump fluids or suitable working fluids or storage fluids for pumps generally and EK pumps specifically?]

The term delivery fluid has been used throughout the description. In many pumping system embodiments, the delivery fluid is any fluid having a viscosity low enough to be pumped through action of the pump element. In some embodiments, the delivery fluid is a pharmacological agent. In other embodiments, the delivery fluid is a therapeutic agent. In still other embodiments, the delivery fluid is a saline solution or Ringers solution.

While numerous embodiments of the present invention have been shown and described herein, one of ordinary skill in the art will appreciate that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. In addition, the intended uses of the present invention include a variety of medical applications as well as other applications where highly precise, compact devices for fluid transport are needed. It should be understood that various alternatives to these embodiments of the invention described herein may be employed in practicing the invention. It is intended at the following claims defined the scope of the invention and it methods and structures within the scope of these claims and their equivalents be covered thereby. 

1. A piston assembly, comprising: A piston housing; A housing within the piston housing that divides the piston housing into a first portion and a second portion, the housing having apertures that provide fluid communication between the first portion and the second portion; A shaft connecting the housing to a piston head outside of the piston housing; and A porous material inside of the housing.
 2. The piston assembly of claim 1 where in the piston housing is filled with an electrolyte.
 3. The piston assembly of claim 1 where in the porous material inside of the housing is in contact with the electrolyte.
 4. The piston assembly according to claim 1 wherein the porous material is a porous dielectric material adapted for operation as part of an electrokinetic pump.
 5. The piston assembly according to claim 1 further comprising: A sealing element around the piston head or the housing.
 6. The piston assembly according to claim 1 further comprising a second shaft connecting the housing to a handle outside of the piston housing.
 7. The piston assembly according to claim 6 further comprising a valve within the second shaft wherein actuation of the valve provides a flow path between the first portion and the second portion.
 8. The piston assembly according to claim 7 wherein the flow path from one side of the housing to the other side of the housing includes a bypass through the porous material contained in the housing.
 9. The piston assembly according to claim 7 wherein the valve is actuatable from a handle attached to the second shaft.
 10. The piston assembly according to claim 1 wherein the shaft extends through a wall in the piston housing.
 11. The piston assembly according to claim 5 wherein the sealing element around the material housing seals the housing to a wall of the piston housing.
 12. The piston assembly according to claim 1 further comprising an electrode in the first portion and an electrode in the second portion.
 13. The piston assembly according to claim 12 wherein the electrodes have a double layer capacitance of greater than 10⁴ microfarad/cm².
 14. A pump, comprising: a delivery chamber, a pump chamber and a wall separating the pump chamber from the delivery chamber; a piston assembly having a piston head in the delivery chamber, a housing in the pump chamber and a shaft connecting the piston head to the housing and passing through the wall separating the pump chamber from the delivery chamber; and a dielectric material in the housing.
 15. The pump according to claim 14 further comprising: a pair of electrodes in the pump housing.
 16. The pump according to claim 15 wherein one electrode is on each side of the housing.
 17. The pump according to claim 15 wherein the pair of electrodes are made from a material selected to electrokineticly move a fluid in the pump chamber.
 18. The pump according to claim 14 wherein the delivery chamber and the pump chamber are in a single housing.
 19. The pump according to claim 14 wherein the housing divides the pump chamber into a first portion and a second portion.
 20. The pump according to claim 19 further comprising apertures in the housing that provide fluid communication between the first portion and the second portion.
 21. The pump according to claim 14 further comprising an electrolyte in the pump chamber.
 22. The pump according to claim 15 wherein each electrode in the pair of electrodes has a double layer capacitance of more than 10⁴ microfarad/cm².
 23. The pump according to claim 14 further comprising: a bypass valve in the shaft that provides a fluid pathway from one side of the housing to the other side of the housing.
 24. The pump according to claim 14 further comprising: a bypass valve in the shaft that provides a fluid pathway from the first portion to the second portion.
 25. The pump according to claim 14 wherein the delivery chamber is filled with a delivery fluid by relative movement between the pump chamber and the delivery chamber.
 26. The pump according to claim 17 wherein application of an electric field across the electrodes moves the fluid in the pump chamber from one side of the housing to the other side of the housing.
 27. The pump according to claim 17 wherein application of an electric field across the electrodes moves the piston head in the delivery chamber.
 28. The pump according to claim 17 wherein application of an electric field across the electrodes moves the housing relative to the pump chamber.
 29. A method for operating a fluid delivery system, comprising: inserting a piston assembly into a delivery chamber, the piston assembly having a pump housing, a piston head outside of the pump housing and attached to a shaft extending through a wall in the pump housing, a housing attached to the shaft and between electrodes in the pump housing; and filling the delivery chamber with a delivery fluid by withdrawing the piston head from within the delivery chamber.
 30. A method for operating a fluid this delivery system according to claim 29, further comprising: fixing the position of the pump housing relative to the delivery chamber.
 31. A method for operating a fluid delivery system according to claim 29 further comprising: advancing the piston head in the delivery chamber by moving fluid in the pump chamber.
 32. A method according to claim 31 wherein moving fluid within the pump chamber comprises electrokineticly moving fluid through the housing.
 33. A method according to claim 31 wherein moving fluid within the pump chamber comprises providing an electric field between the electrodes.
 34. The method according to claim 29 wherein the filling step comprises withdrawing the pump assembly.
 35. A method for operating a fluid delivery assembly having a pump chamber and a delivery chamber, comprising: withdrawing a shaft from within the fluid delivery assembly to simultaneously displace a moving pump element within the delivery chamber and bypass fluid around a housing in the pump chamber.
 36. A method for operating a fluid delivery assembly according to claim 35 wherein withdrawing a shaft from the pump assembly introduces a delivery fluid into the delivery chamber and into contact with the moving pump element.
 37. A method of operating fluid delivery assembly according to claim 35 further comprising: advancing the moving pump element in the delivery chamber by applying an electrical field across electrodes in the pump chamber and on either side of the housing.
 38. A method of operating a fluid delivery assembly according to claim 35, further comprising: electrokineticly moving fluid in the pump chamber to dispense fluid from the delivery chamber.
 39. The method of claim 35 further comprising: Actuating a bypass in the shaft during the withdrawing step. 